1. Field of the Invention
The present invention relates to a laminated electronic component and a method for manufacturing the laminated electronic component, and more particularly, to a laminated electronic component having external electrodes formed by plating directly on an external surface of a laminated body and a method for manufacturing the laminated electronic component.
2. Description of the Related Art
As shown in FIG. 11, a laminated electronic component 101 such as a laminated ceramic capacitor, which is a typical example, usually includes a laminated body 105 including a plurality of laminated insulator layers 102 and a plurality of lamellar internal electrodes 103 and 104 extending along surfaces of the insulator layers 102. End portions of the internal electrodes 103 and 104 are exposed at an end surface 106 and an end surface 107 opposite thereto of the laminated body 105, respectively. External electrodes 108 and 109 are arranged so as to electrically connect the end portions of the internal electrodes 103 to each other and the end portions of the internal electrodes 104 to each other, respectively.
Usually, the external electrodes 108 and 109 are formed by applying a metal paste including a metal component and a glass component to the end surfaces 106 and 107 of the laminated body 105, baking so as to form a paste electrode layer 110, forming a first plating layer 111 including Ni or other suitable metal as a main component on the paste electrode layer 110, and forming a second plating layer 112 including Sn or other suitable metal as a main component on the first plating layer 111. That is, each of the external electrodes 108 and 109 have a three-layer structure including the paste electrode layer 110, the first plating layer 111, and the second plating layer 112.
The external electrodes 108 and 109 need to have good wettability for soldering when the laminated electronic component 101 is mounted on a substrate with solder. Furthermore, the external electrode 108 must electrically connect the plurality of internal electrodes 103 to each other, which are electrically isolated, and the external electrode 109 must electrically connect the plurality of internal electrodes 104 to each other, which are electrically isolated. The second plating layer 112 has a function of ensuring wettability for soldering and the paste electrode layer 110 has a function of electrically connecting the internal electrodes 103 to each other or the internal electrodes 104 to each other. The first plating layer 111 has a function of preventing leaching or wicking in a solder-bonding process.
The thickness of the paste electrode layer 110 is as large as a few tens of μm to a few hundred μm. Therefore, in order to manufacture the laminated electronic component 101 so as to have a desired standard size, an effective volume of the laminated electronic component 101 that determines an electrostatic capacity thereof must be reduced because the volume of the paste electrode layer 110 having the above-mentioned volume is included in the standard size dimensions. In contrast, the thickness of each of the plating layers 111 and 112 is about a few μm. Therefore, if the external electrodes 108 and 109 are formed with the first plating layer 111 and the second plating layer 112 alone, the effective volume of the laminated electronic component 101 that determines an electrostatic capacity thereof can be increased.
For example, Japanese Unexamined Patent Application Publication 2004-146401 discloses a method including applying a conductive paste on an end surface, which includes at least one ridge extending in the direction perpendicular to laminated internal electrodes, of a laminated body, so as to be in contact with extending portions of the internal electrodes, forming a conductive film by baking or thermally curing the conductive film, and then electrolytically plating the end surface of the laminated body so as to form an electrolytic plating film connecting to the conductive film formed on the ridge. According to this method, the thickness of an external electrode at an end surface is reduced.
Japanese Unexamined Patent Application Publication 63-169014 discloses a method for depositing a conductive metal film by electroless plating over side surfaces of a laminated body to connect the internal electrodes to each other, which are exposed on the side surfaces.
When the method for forming an external electrode described in Japanese Unexamined Patent Application Publication 2004-146401 is used, the electrolytic plating film and the exposed internal electrodes can be directly connected. A conductive portion made of conductive paste, however, must be formed in order to electrically connect the extending portions of the exposed internal electrodes before performing electrolytic plating. There are problems with this method for applying the conductive paste to a desired portion of the laminated body and, furthermore, the effective volume rate of the laminated body is decreased because the conductive paste has a large thickness.
On the other hand, when the method for electroless plating described in Japanese Unexamined Patent Application Publication 63-169014 is used, if a material such as Pd having high catalytic activity is not applied on the surface prepared in advance for a plating process, the compactness and homogeneity of the resulting plating film are decreased. This leads to a problem that a plating solution enters inside of the laminated body and the reliability of the laminated body is significantly reduced. Whether a high catalytic activity material is applied or not is not described in Japanese Unexamined Patent Application Publication 63-169014. However, if a homogeneous plating film is formed as described in Japanese Unexamined Patent Application Publication 63-169014, it is highly possible that a material having high catalytic activity is applied in advance. However, the process for adding a catalyst is cumbersome and it has a problem in that a plating film may be easily deposited on undesirable portions.
Furthermore, in the method described in Japanese Unexamined Patent Application Publication 63-169014, the material of the internal electrodes disposed in the laminated body is Pd or Pt. The use of such an expensive metal leads to an increase in the cost of the laminated electronic components.
Furthermore, in the method described in Japanese Unexamined Patent Application Publication 63-169014, the thickness of the internal electrodes must be at least about 1 μm. This leads to an increase in the volume of the laminated body and an increase in the cost of the laminated electronic component.